The Value of an Empirical Approach for the Assessment of Diatoms as Environmental Trace Evidence in Forensic Limnology

Abstract

Environmental trace evidence is often encountered during a forensic investigation and is acknowledged to have the potential to contribute valuable circumstantial information pertaining to the context of an individual criminal event. Although traditional study has focused upon the analysis of terrestrial soil and sediment traces, there is growing potential for the forensic assessment of aquatic crime scenes, particularly those within freshwater environments. This paper outlines the current applications of limnology, particularly algae and diatom analysis, within forensic science and introduces new and ongoing research within the field. Two empirical studies are presented which highlight the importance of developing evidence bases within freshwater trace evidence analysis. These studies demonstrate the analytical capability of the Scanning Electron Microscope (SEM) at various stages of an investigation: in the initial screening and collection of an evidential sample from clothing (1); and in the analysis of preserved diatoms following various levels of their exposure to fire damage (2). The results highlight that the SEM provides a valuable tool during the initial stages of an investigation, determining the presence and abundance of a range of environmental indicators and directing further strategy for the more in-depth collection and analysis of a forensic sample. Furthermore, the preservation of diatoms adhering to clothing following prolonged exposure to fire, indicates that efforts to collect any destroyed evidence are worthwhile given the potential to recover freshwater traces over extended time scales. Finally, the value of adopting an empirical approach for the development of a forensically relevant evidence base within forensic limnology, and the importance of having an appreciation of the legal implications for the interpretation and admissibility of freshwater evidence is presented.

Freshwater diatom transfer to clothing: Spatial and temporal influences on trace evidence in forensic reconstructions

“…This study presents the first application of the H2O2 extraction method for the recovery of diatoms from clothing materials other than 100% cotton [11,15]. Diatoms were successfully retrieved from all nine clothing types examined, although a relatively large standard deviation was sometimes reported between sample triplicates in relation to both the total count (per cm 2 ) and total number of species identified (Figures 3 & 7).…”

“…Despite this initial focus, additional research is required to investigate the transfer and persistence dynamics of diatoms in experimental scenarios pertinent to forensic casework. Such research is imperative to inform the investigative approach taken during the collection and analysis of diatoms recovered from evidential items, and to support the exclusionary interpretation of those findings in a court of law [10,11].…”

“…Diatoms were extracted from three 1cm 2 subsample replicates of each clothing material swatch using the hydrogen peroxide (H2O2) method outlined in Scott et al [11,15]. Briefly, each subsample was added to a centrifuge tube and heated with 20ml of H2O2 (30%) at 70 0 C for 4 h. Following treatment, the fabric sample was removed, rinsed with distilled water, and a few drops of HCl (10%) added to the solution to eliminate any carbonates present.…”

“…Appropriate measures were incorporated throughout to prevent and mitigate any contamination between samples, in line with usual forensic procedures including the preparation of several 'blank' samples (n = 9) [11,15].…”

“…The value of environmental trace materials in forensic reconstructions is increasingly being recognised in casework and the accompanying empirical research bases [9][10][11]. The exclusionary assessment of trace materials transferred between crime scenes and persons or items of forensic interest, often includes environmental indicators as diverse as soil mineral grains [12,13], algae [14,15], pollen [16,17], and microbial communities [18,19].…”